Intravenous and Subcutaneous Pharmacokinetic Modeling to Support the Development of Long-Acting Multipurpose...

Background/Objectives: Women and girls, particularly in sub-Saharan Africa, face high risks for both HIV and unintended pregnancy. Inconsistent condom use underscores the need for new multipurpose prevention technologies (MPTs) that combine HIV pre-exposure prophylaxis (PrEP) and contraception. Long-acting (LA) injectables are especially promising. To this end, an LA cabotegravir (CAB)/medroxyprogesterone acetate (MPA) in situ-forming implant (ISFI) has been developed. We report pharmacokinetic (PK) modeling to characterize CAB and MPA disposition and absorption to support the development of the MPT ISFI. Methods: Female BALB/c mice received single intravenous (IV) or subcutaneous (SQ) bolus doses of CAB or MPA. Sparse plasma samples were collected (~3 mice/timepoint) for PK analysis by LC-MS/MS. Noncompartmental analysis assessed SQ bioavailability. Macroparameterized compartmental PK models were fit to IV data to derive unit impulse responses (UIRs) for each drug. Results: CAB and MPA exhibited 61% and 42% bioavailability, respectively. CAB IV PK was best described by a two-compartment model with macroconstant parameters: A = 16,621 ng/mL, α = 4.52 h^-1, B = 30,206 ng/mL, and β = 0.053 h^-1. MPA IV PK was also best described by a two-compartment model, with A = 2506 ng/mL, α = 10.5 h^-1, B = 439 ng/mL, and β = 0.65 h^-1. These values define the UIR for CAB and MPA. Conclusions: Our IV PK modeling framework fully characterizes CAB/MPA disposition in mouse, enabling downstream deconvolution-based estimation of absorption from controlled-release formulations. This provides a foundation for in vitro-in vivo correlation, facilitating preclinical evaluation of long-acting formulations such as ISFIs.